Originally Posted by Seldomseensmith
My plan is no primer. Sand old gel coat and roll on.
I would never consider not using a primer before coating with a topside paint. I have not used Rustoleum, so maybe they have some special formulation, but all other more commonly used manufacturers, like Epiphanes and Interlux, both recommend it's use, especially if over patched areas, or bare fibreglass, areas. A good primer with any kind of paint, is mostly made of polymers that adhere fast to the surface it is put on, and allow the paint on top a great surface to bond to.
When doing all the prep work needed before painting
, often much more effort than the painting
itself, the little added effort and cost of a primer seems to make sense.
As far as thinning goes, use what is recommended by the manufacturer, if at all. I know with Interlux Brightside, they say you can use up to 10%. It can help the coating level a bit, but too much and you risk getting runs.